LDC2 with -fxray-instrument

Johan Engelen j at j.nl
Mon Jan 21 16:57:57 UTC 2019

On Monday, 21 January 2019 at 14:36:15 UTC, Márcio Martins wrote:
> On Thursday, 17 January 2019 at 00:11:10 UTC, Johan Engelen 
> wrote:
>> OK, got it :-) LLVM 7 changed things a little, so it's broken 
>> with LDC 1.13  [*].
>> For now, you can use LDC 1.12 (LLVM 6). You also have to add 
>> `-L-lstdc++` as compiler flag. So with LDC 1.12, Linux, and 
>> this commandline things work for me:
>> ```
>> ldc2 -fxray-instrument -fxray-instruction-threshold=1 
>> xraytest.d -L-lstdc++
>> XRAY_OPTIONS="patch_premain=true xray_mode=xray-basic 
>> verbosity=1" xraytest
>> ```
>> Happy testing,
>>   Johan
>> [*] XRay was split into several libraries, and we only 
>> copy+link with one of them. You can make things work by 
>> downloading the libs and linking with them.
> Great! Does it mean it will be fixed in next LDC release? :)

Yes: https://github.com/ldc-developers/ldc/pull/2965

> I also played a bit with -finstrument-functions and it works 
> fine for tools like uftrace... However, if you define your own 
> __cyg_profile_func_* functions, it won't work (or be useful), 
> because there is no way to disable instrumenting on these 
> __cyg_profile_func_* functions, so you can imagine what 
> happens. I tried @llvmAttr("no_instrument_function"), 
> supposedly the GCC compatible way to disable instrumentation on 
> these, but it doesn't make a difference.

You need:  pragma(LDC_profile_instr, false), e.g.:
pragma(LDC_profile_instr, false)
void fun () { ... }

> There are few LLVM settings that will make this useful:
> - https://reviews.llvm.org/D40276
> - https://reviews.llvm.org/D39331 (which enables instrumenting 
> after inlining, which is more useful in my use case)
> - https://reviews.llvm.org/D37622 (is has not been merged yet, 
> but necessary, to be able to conveniently call library 
> functions from within the hooks)

These are not too hard to implement in LDC. Whoever is interested 
in working on it, here are some pointers in addition to the LLVM 


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